Semiconductor devices, such as MOS integrated circuits, are easily destroyed by electrostatic discharges. Damaging electrostatic discharges are likely to occur during any of various assembly operations which involve handling the devices. Particularly when the devices are handled as individual units and are not coupled into a grounded circuit, they are likely to inadvertently become a link in an electrostatic discharge path. It is typically during handling operations relating to testing, sorting, inspecting and mounting the devices on circuit substrates that electrostatic energy which unsuspectedly may have accumulated on an operator becomes released through a device to destroy some circuit element in the device. Procedures are implemented at semiconductor device production and assembly facilities to minimize the occurrences of damaging electrostatic discharges. Among these procedures is the wearing of ground straps. Ground straps are attached to electrically conductive, elastic wrist bands worn by assembly workers to couple the workers electrically to a chassis ground, such as a grounded workbench. The connections to the grounded benches are made, for example, by clipping the ends of the ground straps to the benches or by plugging the ends into grounded sockets. Thus, as the assembly workers move about at the assembly benches to perform their operations, electrostatic charges are continually dissipated through the ground straps as they are generated by the workers' movements.
Problems which do occur on a not so infrequent basis are related to the ground straps failing to establish an electrically continuous path from the workers to ground and, because of the inherent passiveness of a well-established ground connection, such a failure going unnoticed until after damage is already done to semiconductor devices. The problem is compounded by some types of semiconductor devices being so sensitive to electrostatic energy that a typical electrostatic discharge sufficiently severe to destroy a device need not be so severe as to be noticeable to the worker who causes the electrostatic discharge.
An electrically open ground strap connection may occur, for example, when a worker first attempts to couple the ground strap to a bench. Unnoticed intervening dielectric substances, such as intervening dielectric particles or, generally, any smudged contact can prevent a functional ground connection from becoming established. Also, the elastic wrist bands may slip over pieces of clothing or may otherwise fail to establish electrically sufficient contact with the skin to cause the ground strap to fail in dissipating on a continual basis any accumulating electrostatic charges.